There are a number of techniques for the purpose of determining interfacial tension in a liquid-liquid system. The Jobe Pat. No. 3,913,385 and corresponding published patent application No. B 351,735 employ a continuous type monitor for hydrocarbon liquids for automatically detecting the presence of a surface active agent in the hydrocarbon liquid, and employ a caustic liquid to form drops in the monitored liquid. The Davis U.S. Pat. No. 4,196,615 employs a tensiometer which measures changes in capacitance between monitored plates as effected by passage of drops of one liquid falling through a body of a second liquid. The Jobe U.S. Pat. No. 3,881,344 measures surface tension of a stream of flowing liquid as a function of the pressure required to form an air bubble below the surface of the liquid. The Jennings, Jr. et al. U.S. Pat. No. 3,483,737 employs apparatus for measuring interfacial tension by the pendant drop method. The Russian reference SU-601-602 (Sakalskii) employs an instrument in which high voltage is used to break up the surface of a liquid, the voltage value at that time being a measure of the surface tension.
Many methods involve withdrawing a sample, preparing for analysis and then making measurement of interfacial tension according to:
(a) pendant drop method--in which one liquid is allowed to grow slowly from a capillary immersed in a second liquid. Either the detached drop is weighed or a photograph is made and an analysis is performed on the shape.
(b) ring method--a ring is immersed to the level of the interface and the ring is slowly pulled out of the interfacial region and the force measured.
(c) spinning drop method--a drop of the lighter liquid is placed in a capillary between columns of the heavier liquid and rotated about the axis; and analysis of the contact angle is made.